One technology that is rapidly coming to the forefront for the formation of microelectronic devices and components is electrochemical deposition, which includes both electroplating and electroless plating of metal to form microelectronic features on a microelectronic workpiece. Though electrochemical deposition has long been employed as a fundamental step in fabrication of multilevel printed circuit boards, application of electrochemical deposition to fill sub-micron interconnect features is relatively recent and poses further additional problems, including the need for more stringent control of the electrolyte bath composition.
Electrochemical deposition is a complex process involving multiple ingredients in the electrolytic bath. If the electrolytic bath is to provide high-quality deposited films (blanket or patterned) on the surface of the substrate, the concentration of several of the constituents of the bath should be maintained. As such, the ability to monitor and control the composition of the bath is one of the important factors in ensuring uniform and reproducible film properties. In semiconductor and microelectronic component applications, the electronic and morphological properties of the metal films are of principal importance in determining final device performance and reliability. The stability of later microfabrication processes in the manufacturing sequence likewise frequently depends on repeatable mechanical properties, including modulus, ductility, hardness, and surface texture of the deposited material. All of these deposit properties are controlled or strongly influenced by the composition of the electrolytic bath.
Measurement and control of proprietary organic compounds that serve to modify the deposit properties through adsorption onto and desorption from the cathode surface during, for example, electroplating, are important since they affect the diffusion rate of metal cations to nucleation and growth sites. These compounds are typically delivered as multi-component packages from chemistry vendors. One of the functions of the additive packages is to influence the throwing power of the electroplating bath: the relative insensitivity of plating rate to variations in cathodic current density across the wafer or in the vicinity of surface irregularities. The throwing power of the electrolyte has an effect on the cross-wafer uniformity of deposited film thickness and the success with which ultrafine trenches and vias (holes) are filled without included seams or voids. Organic additives have also been shown to have substantial effects on mechanical film properties. Detection and quantification of these bath constituents is complicated by the fact that they are effective at very low concentrations in the electrolyte, for example, at several ppm or less.
Bath analysis for microelectronic applications is strongly driven by the need to limit variability and maintain device yields through maintenance of optimized process parameters. One method for controlling such ingredients in an electroplating bath is to make regular additions of particular ingredients based upon empirical rules established by experience. However, depletion of particular ingredients is not always constant with time or use. Consequently, the concentration of the ingredients is not actually known and the level in the bath eventually diminishes or increases to a level where it is out of the acceptable concentration range. If the additive content concentration deviates too far from the target value, the quality of the deposit suffers and the deposit may be dull in appearance and/or brittle or powdery in structure. Other possible consequences include low throwing power and/or plating folds with bad leveling.
An automated chemical management system for managing the chemical content of an electrochemical bath used to deposit a material on the surface of a microelectronic workpiece is set forth. The automated chemical management system includes a dosing system that is adapted to dose an amount of one or more chemicals to replenish a given electrochemical bath constituent in accordance with a predetermined dosing equation. The chemical management system also includes an analytical measurement system that is adapted to provide a measurement result indicative of the amount of the given constituent in the electrochemical bath at predetermined time intervals. The chemical management system uses the measurement results to modify the dosing equation of the dosing system. In this manner, the replenishment operations executed by the chemical management system are effectively refined over time thereby providing more accurate control of the amount of the target constituent in the electrochemical bath.